This invention is directed to a passive transponder and, in particular, to a passive transponder which is programmable after completion of manufacture utilized for monitoring the characteristic of the host into which it is embedded, and more in particular for identifying an animal and its characteristics.
Transponders and scanner systems are well known in the art. These systems include an interrogator which transmits and receives signals from a passive transponder. One such use is a transponder embedded in an animal. The prior art system known from U.S. Pat. No. 4,730,188 includes an antenna which transmits a 400 KHz signal which is received by the transponder embedded in the animal and returns a divided signal of 40 KHz and 50 KHz. This signal is coded in accordance with a combination of 40 KHz and 50 KHz portions of the transmitted signal to correspond to a preprogrammed ID number stored in a chip contained within the passive transponder. The ID number is preprogrammed at the time of manufacture. This ID number allows identification of the animal in which the transponder is embedded. The scanner then inputs this coded ID number into a microcomputer for processing.
The prior art transponders have been less than completely satisfactory because the amount of information which may be transmitted thereby was limited to the preprogrammed identification numbers contained therein. Accordingly, in a contemplated use such as animal identification, the user must use the preprogrammed identification number to identify the test animal. However, identification numbers are usually used as shorthand manner for presenting data concerning the animals. This requires that the user match his animal information to the preassigned transponder identification number resulting in an increase of time and effort. Additionally, this prior art device is unable to automatically transmit system status information, such as muscular pressure or temperature of the animal. Accordingly, the amount of information transmitted is quite small.
Because the transponders divide the received signal, a high frequency received signal must be broadcast to the transponder so that the divided signal will have a high enough frequency to transmit information. These higher frequencies are regulated by the FCC, therefore, the amount of power which can be supplied to the transponder, and in turn the read distance is limited. Additionally, because the transponder transmit antenna operates at 40 KHz, it is subject to background noise interference from television monitoring screens or computer CRTs which by necessity are normally present since they are used in conjunction with microprocessors which are used during scanning. These monitors also operate utilizing a 40 KHz and 50 KHz RF signal. Because these monitors have a high power output relative to the antenna they interfere with the operation of the interrogator when the interrogator is used in proximity to computers and other various monitors.
Therefore, a passive transponder which simultaneously senses an environmental condition and transmits this information along with user programmable identification information in a manner which is less susceptible to background noise interference is provided by the instant invention.